The 2010 National Health Objectives call for a reduction in the prevalence of obesity. The marked recent increase in overweight and obesity prevalence implicates behavioral factors in the etiology of the epidemic. The present proposal hypothesizes the trend is attributable, in part, to increasing consumption of energy yielding beverages since they are a significant and increasing source of dietary energy and they elicit weaker appetitive and dietary responses than solid foods. Three human studies are proposed to more fully characterize attributes of liquids and solids that may account for the differential appetitive responses they elicit, potential contributory mechanisms as well as the dietary implications of their consumption. Study 1 will contrast the acute effects of fluid and solid foods varying in macronutrient content on satiation, satiety and feeding. Study 2 will determine if the pattern of fluid and solid item ingestion influences satiety and feeding by monitoring appetitive and dietary responses to energy- and macronutrient-matched fluid and solid loads ingested as meal components or between meal "snacks." To better assess the clinical implications of diets incorporating liquid or solid supplements, study 3 will entail chronic ingestion of matched energy-yielding fluid or solid loads with concurrent measurement of appetite, dietary intake, energy expenditure and body weight/composition. Because carbohydrate is the predominant source of energy in beverages and contributes disproportionately to the increasing level of energy intake, our initial search for a mechanism underlying the differential responses to fluid and solid foods relates to carbohydrate metabolism. A critical review of the literature and pilot studies suggest the glucose, insulin, leptin, neuropeptide-Y cascade may be involved and will be targeted for evaluation as part of study 3. We also have evidence implicating cholecystokinin so, this peptide will be assessed. All studies will be conducted with lean and obese individuals to explore the possibility that weaker responses to fluids by the obese may be especially problematic for energy balance in this group. This novel hypothesis regarding a differential response to energy-yielding fluid and solid foods stems from a solid scientific literature and should yield new insights for management of one of the nations most serious public health problems.